Precision Voltage Measurements and the Revised SI Units

Synopsis : Since May 20, 2019, new definitions for four of the seven base units of the International System of Units (SI) have been implemented worldwide. In the new definitions, the unit of electric current, ampere, is defined as the number of electrons flowing in unit time, whereas the value of elementary charge is defined as a constant without uncertainty. This paper focuses on the SI units of electrical quantities and reviews the realization of the unit of voltage, volt, based on the Josephson voltage standard system that uses a cryocooler. Furthermore, this paper reviews the influences of the revised SI units on precise electrical measurements.